The present invention relates to the preparation of printing plates. More particularly, the invention provides a method and apparatus for preparing printing plates which do not require a photomask formed from a sheet of photographic film bearing either the positive or negative of an image to he printed.
A number of methods and apparatus are known for the preparation of printing plates. Typically, such plates are formed by placing a sheet of photographic film hearing either the positive or negative of the particular image to he printed over a substrate coated with a light-sensitive emulsion. The emulsion is then exposed using the film as a photomask. If the emulsion is of the type generally referred to by those skilled in the art as a "negative acting emulsion", the regions of the emulsion not covered by the image on the photomask are hardened and fixed to the substrate when the emulsion is exposed. If the emulsion is a so-called "positive acting emulsion", the regions of the emulsion not covered by the image on the photomask are softened during exposure, while those regions lying beneath the image on the mask remain hard and fixed to the substrate.
In either case, subsequent to exposure the soft or un-hardened regions of the emulsion are washed from the substrate, leaving a pattern of hardened emulsion supported on the substrate. This pattern of hardened emulsion supported by the substrate forms the printing plate which may then used in any manner typically employed by those skilled in the art to print either the positive or negative of a desired image.
The above-described process presents a number of disadvantages. First, either the positive or negative of the image to be printed must be formed on the photographic film. Then, the film must be transferred and properly positioned on the substrate in order to expose the emulsion and form the printing plate. Such a procedure is both time consuming and labor intensive, which adds to the overall cost of the printing plate.
It is, therefore, an object of the invention to provide a method for preparing a printing plate which eliminates the need for making and positioning a photomask formed from a sheet of photographic film.
It is a further object of the invention to provide an apparatus for carrying out such a method.